My builder installed a fresh air timer on my furnace, a 24-hour pin timer with 15-minute increments. When it's on, it runs the fan and opens the fresh air damper. The resulting air that comes from the registers is cold (it's cold outside) but not as cold as the outside air, which leads me to believe it's mixing the outside air with recirculated air from inside.

We ran it on always-on mode for a while to help with the carpet and paint fumes, but it's cold enough outside now that the constant cold air is bothersome. How often/how long/at what times should I run it during different times of the year? The settings the builder left on the timer were clearly the result of someone just haphazardly poking a few groups of pins so it ran a few hour-long intervals every day.

I've poked around on the web a bit but there's an amazing amount of jargon and conflicting advice out there.

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Generally, the seasons is not a determining factor for how much fresh air is required. Rather, other factors such as: 1) exposure to radon, 2) smokers, 3) number of occupants, and 4) type of heating/cooling system.

The Code requires fresh air, but the Code allows operable windows or mechanical fresh air venting.

Usually, if fresh air is provided, it’s connected to the return air system (duct) in a forced air system. That way, when the thermostat calls for heat, the system will bring in fresh air, mix it with recirculated (return) air and then heat it to the desired temperature...as set by your thermostat. That way you won’t have just cold outside air introduced into the rooms.

For radiators or floor heating systems, a fresh air intake system can be installed.

However, where you live, an automatically vented system is very unusual. If you want fresh air, you can just open a window for a couple of minutes and the wind will “purge” the room.

Also, radon is not a consideration where you live.

Oh, by the way, the location of the outside air intake should be at least 10’ from any exhaust vent (duct or plumbing vent) so fumes from such vents are not recirculated back into the residence.


In our area, these systems are required to make sure that your house has sufficient fresh air to combat sick building syndrome. The amount of fresh air required is based on a lot of sophisticated equations of square feet, number of occupants, etc. But after all that, not one word is mentioned about how long it should run in a given 24-hour period. It is totally left up to the home owner. If you have an active house hold with the doors opening several times a day with normal coming and going. You don't need any additional fresh air. If you are a shut-in with very little coming and going, I would say 15-minutes twice per day.

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